Dr. [REDACTED] was researching an anomalous phenomenon until something went wrong, erasing himself and the phenomenon from existence. He was brought back due to a time paradox; if he didn't exist, how would've the phenomenon destroyed itself?
I imagine the anomaly would be classified as Annata, as it would be able alter the universe in a YK-Scenario, but I'm not sure if this classification is really used.
Love to hear feedback!

Dr. [REDACTED] was researching an anomalous phenomenon until something went wrong, erasing himself and the phenomenon from existence.

So what would the SCP article be about? Is doctor redacted the thing in containment? Why? He himself was affected by an anomaly, but he himself is not anomalous.

He was brought back due to a time paradox; if he didn't exist, how would've the phenomenon destroyed itself?

I don't see the time paradox, unless you're saying that the anomaly and the doctor were erased from all time ever. In which case, there still might not be that huge of a gap since the anomaly and the dude were "erased" at the same time—the new timeline would just have neither of them exist at all as if nothing ever happened involving them, right?

I imagine the anomaly would be classified as Annata, as it would be able alter the universe in a YK-Scenario, but I'm not sure if this classification is really used.

I've never seen that object class before, and according to the SCP wiki's searchbar, it doesn't appear in any mainlist pages. A lot of people will downvote for classes outside the typical SEKT system though, so if you really want to use your own special new class, there should be some sort of narrative reasoning for it. Potential for a k-class scenario doesn't really give the reader an idea of how difficult it is to contain the anomaly.

I personally am not too sure about this. Keep in mind that as the author, you know the entire story, but the Foundation needs to have discovered what it knows about the SCP object through observation and experimentation. You'll need to convince your reader that someone with no prior knowledge whatsoever of the anomaly managed to somehow figure out (not magically know!) all the information you've got in the article.

From the Foundation's standpoint, all that they'd have here is some confused guy who nobody remembers saying he was studying an anomaly that no one knows about. Maybe it would make for a workable tale, but I don't really see how it would work for an article.

I see what you mean! You see, Dr redacted was turned into an incorporeal time entity whose physical matter is made up of Bose Einstein condensate. He is not visible without a Hyperspectral Imaging Camera. He can't be physically interacted with but is contained with a incorporeal vacuum chamber and non-physical displacement neuralizers. He is capable of opening portals to different realities, but this is prevented with a scantron reality anchor.

For how the Foundation knows this, I have to add some more work into it.

As of Class Annata, I saw it in the forum under the title of SCP Objects Classifications, and it mentions lots of unused classes, such as Yggdrasil, Truculent, Simpatico, and Mild.

Dr redacted was turned into an incorporeal time entity whose physical matter is made up of Bose Einstein condensate. He is not visible without a Hyperspectral Imaging Camera. He can't be physically interacted with but is contained with a incorporeal vacuum chamber and non-physical displacement neuralizers. He is capable of opening portals to different realities, but this is prevented with a scantron reality anchor.

Yeah, uh… this is really complicated. Might lose some readers with this sort of jargon-heavy premise, and that makes it all the more difficult for the in-universe Foundation to find the guy, especially if he happened to rephase back into existence in a place that doesn't have access to all the equipment needed to just see him to begin with.

As of Class Annata, I saw it in the forum under the title of SCP Objects Classifications, and it mentions lots of unused classes, such as Yggdrasil, Truculent, Simpatico, and Mild.

Those are classes suggested by a person and never adopted; the two articles they adapt to said class have normal SEKT object classes. I recommend not using the other person's custom object class since there isn't really a good reason to do so here. For one, most people won't be familiar with it at all, and given that your object is already very complex, adding on an esoteric object class might just give the impression that there's a bunch of stuff added "because it sounds cool" rather than for the sake of telling an interesting story to the audience.